Composite structures are widely used as high-strength, low-weight materials to replace metals, such as in aerospace applications. A composite structure (e.g., a composite laminate) is formed by one or more composite layers (also referred to as plies or lamina). Each composite layer includes a reinforcement material and a matrix material. The reinforcement material may include fibers. The fibers may be oriented in a single direction (e.g., uni-directional) or in two directions (e.g., bi-directional). The matrix material may include a resin.
Bundles of fibers may be laid up in layers to form a reinforcement layup (also referred to as a preform). The resin is infused within spaces defined between the fiber bundles of the preform to form an integrated preform. The preform may be referred to as a wet preform when the fiber bundles have been pre-impregnated with resin or a dry preform when no resin is present. The integrated preform may be partially cured or fully cured to form the composite structure. One example of a composite structure is a carbon fiber-reinforced polymer.
Surfacing veils may be used in composites to impart certain functional characteristics to the composite structure. A veil is a non-woven, thin mat made from short, chopped filaments (e.g., polyester, fiberglass, or nylon filaments) that are held together using a binder (e.g., a thermoplastic binder). For example, veils may be used on an exterior of the composite structure to help absorb resin and provide a resin rich layer that can help protect the composite from ultraviolet light, corrosion, or water absorption and/or may be used between composite layers (e.g., plies) to increase interlayer (e.g., interply) toughness. However, in order to achieve suitable veil stability; filament lengths, the volume of short filaments, and/or the amount of binder is usually increased. These changes can lead to a reduction in functionality, an increase in thickness or an increase in areal weight of the veil and, thus, the composite structure.
Further, additional surface and/or interlayer modifiers (e.g., binders, resin modifiers, particulate additives, and/or surface treatments) may be used in composites to impart certain functional characteristics to the composite structure. However, incorporation of such surface and/or interlayer modifiers may have a negative impact on the resin in the composite structure, mechanical performance of the composite structure, and/or cost of the composite structure.
Accordingly, those skilled in the art continue with research and development efforts in the field of improving the stability and/or the functionality of composite structures.